This disclosure relates to a method and system for welding tools such as those used for moulding and stamping. More particularly, the disclosure relates to a method and system for welding additional material onto a tool to be reworked, for example, for subsequent use in producing products in need of a class A surface.
Tools, such as stamping tools and plastic injection moulds, must be welded for a variety of reasons. During the repair of tools for cracks or wear, it is often necessary to grind out material and then build up the ground surface to provide new material. The newly welded material is then partially machined away to create a new surface that matches the required design surface.
Additionally, there are occasionally part changes that deviate from the initial part design. Part changes require a corresponding change in the tool. If this change involves only the removal of material from the tool, then material can be simply machined away. If however the part design change requires addition of material to the surface of the tool, as it typically does, then additional material must be added to the desired area. This is accomplished through the application of successive layers of weld material until the required thickness of material is added prior to machining. The required thickness of material may be as high as 2 inches (50 mm) requiring numerous layers of weld material to be applied.
Because of the high surface quality required for many tool surfaces (particularly those being built to Class A automotive standards), and the additional risk of distortion of the welded surface, the tool must be welded using tungsten inert gas (TIG) welding at an elevated temperature of approximately 700° F. (370° C.). When such welding is carried out using manual techniques, the welder must be provided with protective gear and suitable cooling when working in this very harsh environment. Often the tool can only be heated to approximately 400° F. (210° C.), which is less than desired, to accommodate the welder.
Robotic welding has been experimented with in various fields of industry. For example, robotic welding systems for rapid prototyping have been suggested. Such systems have been very conceptual in nature and do not lend themselves to the unique environment and challenges of welding tools that require class A surfaces. These large tools, typically weighing several tons, thermally expand as much as a half an inch (12 mm) or more as they are heated.
A typical application in tool modification is to build up a rectangular, circular, triangular, or arbitrarily shaped area on the surface on the tool. This is accomplished by laying down parallel passes of weld metal on the area to be built up and then repeating this process to build up multiple layers, one at a time, until the required metal thickness is achieved. This is a very time consuming process and requires the investment of substantial man hours of welding in order to achieve the required surface shape. A highly skilled tool welder can typically only weld about a half a pound of material per hour. The boundary of the manually welded area typically varies such that a more than desired amount of welded material must be removed during final machining. This is because a typical welder cannot achieve and maintain the contour of the outer boundary throughout the welding process. Manual welders sometimes weld a perimeter as a guide so that they more accurately lay down the desired weld shape to the area.
What is needed is an automated welding method and system that is suitable for tool welding in heated environments.